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Front-wheel drive

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Front-wheel drive is the most common form of engine/transmission layout used in modern passenger cars, where the engine drives the front wheels. Most front-wheel drive vehicles today feature transverse engine mounting, whereas in past decades engines were usually positioned longitudinally as they had been in rear-wheel drive vehicles. Rear-wheel drive had been the traditional standard, and is still used in some luxury cars, sport cars, and most trucks. Four-wheel drive is also increasingly common.

History

1900 - 1920

Experiments with front-wheel drive cars date to the early days of the automobile. Following the Spanish-American War, J. Walter Christie of the USA was working on designs for a front-wheel drive car, which he promoted and demonstrated by racing at various speedways in the US, and even competed in the Vanderbilt Cup and the French Grand Prix. In 1912 he began manufacturing a line of wheeled fire engine tractors which used his front-wheel drive system, but due to lack of sales this venture failed.

1920 - 1930

The first successful application of front-wheel drive was the Miller 122 racecar designed in 1924 by Harry Arminius Miller of Menomonie, Wisconsin. However, the idea languished outside of the motor racing arena as no major auto manufacturer attempted the same for production automobiles. Market experiments in the United States were left to small endeavors such as the Ruxton (200 cars in 1929), and the Cord L-29 of 1929. Neither automobile maker was particularly successful on the open market. Alvis Cars of the United Kingdom also introduced a front-wheel drive model in 1928, but it was not a success either.

1930 - 1945

The first successful consumer application came in 1931 with the DKW F1 from Germany, and in 1934 with the Traction Avant cars by Citroën of France. BSA three-wheelers of the United Kingdom were also popular front-wheel drive automobiles, and the Cord 810 of the United States managed a bit better in the late 1930s than its predecessor one decade earlier. These vehicles featured a layout that places the engine behind the transmission, running "backwards," (save for the Cord, which drove the transmission from the front of the engine). The basic front-wheel drive layout provides sharp turning, and better weight distribution creates "positive handling characteristics" due to its low polar inertia and relatively favourable weight distribution. (The heaviest component is near the centre of the car, making the main component of its moment of inertia relatively low). Another result of this design is a lengthened chassis.

1945 - 1960

Front-wheel drive was further popularized by the 1948 Citroën 2CV,[citation needed] where the lightweight aluminium flat twin engine was mounted ahead of the front wheels, and 1955 Citroën DS, featuring the mid-engine layout. Panhard of France, DKW of Germany and Saab of Sweden offered exclusively front-wheel drive cars.

1960 - 1975

The transversely mounted engine combined with front-wheel drive was popularized by the 1959 Mini;[citation needed] there the transmission was built into the sump of the engine, and drive was transferred to it via a set of primary gears. The same transmission concept was also used by Peugeot and Renault on their jointly-developed small car engine of the 1970s where the 4-cylinder block was canted over to reduce the overall height of the engine with the transmission underneath. The tendency of this layout to generate unwanted transmission "whine" has seen it fall out of favour.

The 1965 Triumph 1300 was designed around a longitudinal engine with the transmission underneath. Audi has also used a longitudinally mounted engine overhung over the front wheels since the 1970s. Also in the 1970s and 1980s, the Douvrin engines used in the larger Renaults (20, 21, 25 and 30) used this longitudinal "forward" layout. The first generation Saab 900, launched in 1978, also used a longitudinal engine with a transmission underneath with helical gears. Audi is one of the few manufacturers which still uses this particular configuration. It allows the use of equal-length half shafts and the easy addition of all-wheel drive, but has the disadvantage that it makes it difficult to achieve 50/50 weight distribution (although they remedy this in four-wheel drive models by mounting the gearbox at the rear of the transaxle.)

The 1966 Oldsmobile Toronado was the first U.S. front-wheel drive car since the Cord 810. It used a longitudinal engine placement for its V8, coupled with an unusual "split" transmission, which turned the engine power 180 degrees. Power then went to a differential mounted to the transmission case, from which half-shafts took it to the wheels. The driveline was set fairly at centre-point of the wheels for better weight distribution, though this raised the engine, requiring lowered intake systems.

1975 - 1990

The Corporate Average Fuel Economy standard drove a mass changeover of cars in the US to front-wheel drive. The change began in 1978, with the introduction of the first American-built transverse-engined cars, the Plymouth Horizon and Dodge Omni (based on the European designed Simca Horizon),[1] followed by the 1980 Chevrolet Citation and numerous other vehicles. By reducing drivetrain weight and space needs, vehicles could be made smaller and more efficient without sacrificing acceleration. Some suggest that the introduction of the modern Volkswagen Rabbit in 1975, from a traditional U.S. competitor, served as a wake-up call for the "Big Three" (which already produced front-wheel drive vehicles in their operations outside North America). Front-wheel drive became the norm for mid-sized cars starting with the 1982 Chevrolet Celebrity, 1983 Dodge 600, 1985 Nissan Maxima, and the 1986 Ford Taurus. By the mid-1980s, most formerly rear-wheel drive Japanese models were front-wheel drive, and by the mid-1990s, most American brands only sold a handful of rear-wheel drive models.

1990 - today

There were relatively few rear-wheel drive cars by the early 1990s; Chrysler's car line-up was entirely front-wheel drive by 1990.

The vast majority of front-wheel drive vehicles today use a transversely mounted engine with "end-on" mounted transmission, driving the front wheels via driveshafts linked via constant velocity (CV) joints. This configuration was made popular by the 1967 Simca 1100,[2] and the 1969 Fiat 128.[citation needed] The 1959 Mini, while a pioneering transverse front-wheel drive vehicle[citation needed], used a substantially different arrangement with the transmission in the sump.

American auto manufacturers are now shifting larger models (such as the Chrysler 300 and most of the Cadillac lineup) back to rear-wheel drive.[3][4]

Records

  • The Cadillac Eldorado, with front-wheel drive introduced in 1967, holds the record for the largest engine in a front-wheel drive production vehicle, at 8.2 L (500 in³), starting with the 1970 model, lasting until the 1976 model year.[citation needed]
  • In acceleration, the Dodge SRT-4 holds the world record for the quickest front-wheel drive production vehicle.[5]
  • A turbocharged Citroën SM broke the land speed record for its class at Bonneville Salt Flats in Utah in 1987, going 202 mph (325 km/h), a record for a front-wheel drive vehicle.[6]

Advantages of front-wheel drive

  • Interior space: Since the powertrain is a single unit contained in the engine compartment of the vehicle, there is no need to devote interior space for a driveshaft tunnel or rear differential, increasing the volume available for passengers and cargo.[7]
  • Cost: Fewer components overall.[7]
  • Weight: Fewer components mean lower weight.
  • Improved fuel efficiency due to less weight.
  • Improved drivetrain efficiency: the direct connection between engine and transaxle reduce the mass and mechanical inertia of the drivetrain compared to a rear-wheel drive vehicle with a similar engine and transmission, allowing greater fuel economy.[7]
  • Assembly efficiency: the powertrain can often be assembled and installed as a unit, which allows more efficient production.[citation needed]
  • Placing the mass of the drivetrain over the driven wheels moves the centre of gravity farther forward than a comparable rear-wheel drive layout, improving traction and directional stability on wet, snowy, or icy surfaces.[7][8][9]
  • Predictable handling characteristics: front-wheel drive cars, with a front weight bias, tend to understeer at the limit, which, for less-advanced drivers, may be easier to correct than oversteer, and less prone to result in fishtailing or a spin.[9][10]
  • The driver can control the movementum of the car even while skidding by steering, throttling and pulling the hand brake (given that the hand brake operates the rear wheels).[11][dubious – discuss]
  • According to a sales brochure for the 1989 Lotus Elan, the ride and handling engineers at Lotus found that "for a given vehicle weight, power and tire size, a front wheel drive car was always faster over a given section of road."[12] However, this may only apply for cars with moderate power-to-weight ratio.[8][13][14][dubious – discuss] According to road test with two Dodge Daytonas, one FWD and one RWD, the road layout is also important for what configuration is the fastest.[9]
  • It is easier to correct trailing-throttle or trailing-brake oversteer.[9]

Disadvantages of front-wheel drive

  • Torque steer is the tendency for some high power front-wheel drive cars to pull to the left or right under hard acceleration. It is a result of the offset between the point about which the wheel steers (which falls at a point which is aligned with the points at which the wheel is connected to the steering mechanisms) and the centroid of its contact patch. The tractive force acts through the centroid of the contact patch, and the offset of the steering point means that a turning moment about the axis of steering is generated. In an ideal situation, the left and right wheels would generate equal and opposite moments, cancelling each other out, however in reality this is less likely to happen. Torque steer can be addressed by using a longitudal layout, equal length drive shafts, half shafts, a multilink suspension or centre-point steering geometry.[15][16][17][18][19][20][21][22]
  • Lack of weight shifting will limit the acceleration of a front-wheel drive vehicle. In a vehicle, the weight shifts back during acceleration, giving more traction to the rear wheels. This is one of the main reasons why nearly all racing cars are all- or rear-wheel drive. However, since front-wheel drive cars have the weight of the engine over the driving wheels, the problem only applies in extreme conditions.
  • In some towing situations, front-wheel drive cars can be at a traction disadvantage since there will be less weight on the driving wheels. Because of this, the weight that the vehicle is rated to safely tow is likely to be less than that of a rear-wheel drive or four-wheel drive vehicle of the same size and power.
  • Traction can be reduced while attempting to climb a slope in slippery conditions such as snow or ice covered roadways.
  • Due to geometry and packaging constraints, the CV joints (constant-velocity joints) attached to the wheel hub have a tendency to wear out much earlier than the universal joints typically used in their rear-wheel drive counterparts (although rear-wheel drive vehicles with independent rear suspension also employ CV joints and half-shafts). The significantly shorter drive axles on a front-wheel drive car causes the joint to flex through a much wider degree of motion, compounded by additional stress and angles of steering, while the CV joints of a rear wheel drive car regularly see angles and wear of less than half that of front wheel drive vehicles.
  • The driveshafts may limit the amount by which the front wheels can turn, thus it may increase the turning circle of a front-wheel drive car compared to a rear-wheel drive one with the same wheelbase.
  • Due to the combined stress of steering and power, the front tires have a tendency to wear more quickly when compared with rear-wheel drive vehicles.[citation needed]

References

  1. ^ Bryan T. Nicalek. "The Dodge Omni and Plymouth Horizon". Allpar.
  2. ^ Andy Thompson and Matt Cotton. ""Simca 1000 cars"". Rootes-Chrysler.co.uk.
  3. ^ "The Chrysler-Dodge LX Cars: Charger, Challenger, 300, 300C, and Magnum". Allpar.
  4. ^ "Cadillac goes to RWD - rear-wheel drive". Automotive Industries (extracted in LookSmart).
  5. ^ Dodge
  6. ^ Infoweb
  7. ^ a b c d Inside Line: What Wheel Drive?
  8. ^ a b William, Milliken (1995). "Merits of Front-, Rear-, and Four-Wheel Drive". Race Car Vehicle Dynamics. SAE International. p. 730. ISBN 1560915269. Front-wheel drive has been most successful in the lower power/weight range and in sutuations in which superior derectional stability on low coefficients is important. There has never been a successful front-drive Grand Prix car nor a competitive Indianapolis car of more than 300 hp.
  9. ^ a b c d "What's It Like To Drive", describes a test between two Dodge Daytonas, one FWD and one RWD
  10. ^ The Hidden Virtues of Front Wheel Drive
  11. ^ Modern Racer: Front-Wheel-Drive Oversteer
  12. ^ Lotus Elan M100 Sales Manual
  13. ^ Frere, Paul (1992). "From Slipping to Sliding". Sports Car and Competition Driving. entleyPublishers. pp. 67pp. ISBN 0836702025. Front-wheel drive which, due to the reduced front wheel grip under acceleration, is practical only for cars of moderate power-to-weight ratio {{cite book}}: Check |isbn= value: checksum (help)
  14. ^ Prost, Alain (1990). "Controlling a car at the limit". Competition Driving. Hazelton Publishing. pp. 50pp. ISBN 0905138805. Front-wheel drive. In this instance, both power and steering are directed through the front wheels, the rears remaining free. Following the principle of weight transfer once more, the lightening of the front wheels under acceleration considerably reduces their effectiveness and thus limits the usable power. Consequentally, this type of transmission is generally less effective on racing circuits, a few rare exceptions notwithstanding, but has its advantages in road events where maximum power is not called into play so often
  15. ^ Jens Dornhege. "Torque Steer Influences on McPherson Front Axles" (PDF).
  16. ^ "What is Torque Steer?". MPH Magazine.
  17. ^ "Handling". AutoZine Technical School.
  18. ^ "Technobabble: Multilink and the Beam". Sport Compact Car - November '98.
  19. ^ "Suspension Geometry". AutoZine Technical School.
  20. ^ "Why use Quaife?".
  21. ^ "Storm Transmission Modifications".
  22. ^ Paul Yih. "Vehicle State Estimation Using Steering Torque" (PDF). Stanford University.
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